1. Field of the Invention
This invention relates generally to the field of gas or air drying devices and more particularly to regenerative gas or air drying devices which utilize desiccant to dry air or other gases in a chamber in one portion of the device in which wet air or gas is passed through the desiccant contained in such chamber and the moisture is adsorbed by the desiccant and in another portion of the device microwaves are dispersed through another chamber containing saturated desiccant, which had become saturated in previously drying wet air or gas, to increase the temperature of the moisture that was adsorbed by the desiccant to enhance the drying of the desiccant for reuse to again dry wet air or gas.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
Drying devices receiving a gas under pressure such as air containing a high level of moisture are well known. These gas drying devices are commonly used in many industrial applications such as painting, pneumatic control systems and air operated equipment. It is also known in such devices to utilize a desiccant such as activated alumina, carbons, silica gels or molecular sieves located in a chamber to adsorb and remove the moisture from the inlet wet air or gas that is under pressure. Such air drying devices frequently use a portion of the dried air or purge gas from one desiccant chamber that is drying air to regenerate the desiccant in another chamber that has already removed moisture from the wet air in a previous cycle. The portion of dried air or purge gas is often diverted to a heater to elevate the temperature of the purge gas. Thereafter, the heated purge gas is moved to the other desiccant chamber to dry out and regenerate the saturated desiccant located therein.
Referring to FIG. 1, a known regenerative gas drying device is shown receiving wet gas (shown as solid arrows) through inlet 10. The wet gas enters a chamber 12 through screen 13 which is filled with desiccant 14. As the wet gas migrates through chamber 12, moisture in the gas is adsorbed by desiccant 14 thereby drying the gas. The dried gas (shown as hollow arrows) exits chamber 12 through screen 15 and is carried to gas outlet 16, at which, the dried gas leaves the drying device. However, not all of the dried gas exits the device for use. A small portion of the gas or commonly called purge gas is diverted into transport pipe 18 and is carried to heater 20.
The purge gas is heated at heater 20 and subsequently, is transported to another chamber 22 and enters chamber 22 through screen 23. Chamber 22 is filled with desiccant as in the first chamber 12, however, desiccant 14 in chamber 22 is saturated with moisture from a previous air drying cycle. The heated purge gas dries saturated desiccant 14 in chamber 22. The high moisture air from the drying of desiccant 14 in chamber 22 is removed from chamber 22 through screen 25 and exits the air drying device at exit valve 24.
Once desiccant 14 in chamber 12 is saturated from an air drying cycle and desiccant 14 in chamber 22 is dried out, the cycle is reversed by flipping diverter valves 25A and 25B. The wet gas is dried and heated upon passing through chamber 22 and heater 20. The dry and heated purge gas from chamber 22 is, in turn, used to dry the saturated desiccant of the first chamber 12. These known systems normally utilized approximately 7 percent of total dried air for the purge gas to regenerate desiccant. The regenerative gas drying device is cycled in this manner to continuously dry out the wet gasses.
Many problems arise in using these known systems. A large percentage of the dried air is utilized for purge which is needed to regenerate the desiccant. In addition, the purge is heated by heaters which utilize large quantities of energy and operate at very high temperatures. The high temperatures can precipitate further fire hazards particularly when such heaters are in close proximity to oil lubricated compressors used in conjunction with these systems to pressurize the desiccant chambers.
It is also known in gas drying systems to send microwave energy into pressurized tanks to heat gases adsorbed by desiccant materials located therein. In U.S. Pat. No. 4,312,640 to Verrando issued Jan. 26, 1982, and U.S. Pat. No. 4,312,641 to Verrando et al. issued Jan. 26, 1982, microwave energy is passed through microwave pressure windows and into tanks carrying sorbent or desiccant material. The microwaves are used to release and remove a polar gas adsorbed by sorbent or desiccant material in the tanks. The microwave energy is prevented from being sent into the tanks in response to the desorbtion of the moisture from the sorbent material. Purge gas is still moved through the desorbed desiccant until the moisture level of the chamber is adequately lowered.
In U.S. Pat. No. 4,322,394 to Mezey et al. issued Mar. 30, 1982, microwave energy is used to dielectrically heat saturated solids of noncarbon adsorbents for the removal of adsorbed materials. The microwaves heat the adsorbents internally to bring the adsorbents to a temperature for desorbing some of the adsorbate in the absence of any activating or purge gas.
Disadvantageously, in these known systems the distribution of the microwave energy within the pressurized tanks is limited. The microwave energy sent through pressure windows adjacent the tank enhances the ability of removal of the adsorbed material proximate to the pressure windows. However, since these known air drying systems do not provide a means for dispersing the microwaves throughout the tank, the material adsorbed by the desiccant located away from the pressure windows does not get sufficiently energized by the microwave to efficently desorb the adsorbate material. Thus, efficient desorbtion of wet gas is achieved more effectively at locations proximate to the pressurized windows while desiccant further away from the pressure windows does not receive as effective and beneficial microwave energy for desorbtion.